Flow measurement apparatus having strain-based sensors and ultrasonic sensors

ABSTRACT

A flow measurement apparatus is provided that combines the functionality of an apparatus that uses strain-based sensors and ultrasonic sensors to measure the speed of sound propagating through a fluid flowing within a pipe, and measure pressures disturbances (e.g. vortical disturbances or eddies) moving with a fluid to determine respective parameters of the flow propagating through a pipe. The apparatus includes a sensing device that includes an array of pressure sensors used to measure the acoustic and convective pressure variations in the flow to determine desired parameters and an ultrasonic meter portion to measure the velocity and volumetric flow of the fluid. In response to an input signal or internal logic, the processor can manually or dynamically switch between the pressure sensors and ultrasonic sensors to measure the parameters of the flow. The flow measurement apparatus thereby provides a robust meter capable of measuring fluid flows having a wide range of different characteristics and flows exposed to different environmental conditions.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.10/964,043 filed on Oct. 12, 2004, which will issue into U.S. Pat. No.7,237,440 on Jul. 3, 2007, which claimed the benefit of U.S. ProvisionalPatent Application No. 60/510,218 filed Oct. 10, 2003, which areincorporated by reference herein in their entirety.

TECHNICAL FIELD

This invention relates to an apparatus for measuring a parameter of aprocess flow passing within a pipe, and more particularly to a flowmeasurement apparatus having ultrasonic sensors and an array ofstrain-based sensors and for processing data signals therefrom toprovide an output indicative of the speed of sound propagating throughthe process flow and/or a flow parameter of the process flow passingthrough a pipe.

BACKGROUND ART

Ultrasonic flow meters are well known for measuring volumetric flow ofliquids and gas. Ultrasonic meters may be mounted within a pipe, mountedwithin a spool piece, or clamped onto the outer surface of the pipe.While ultrasonic meters are suitable and in some case accurate flowmeters, such as gas custody meters, ultrasonic meters are not suitablefor all fluid flows. For instance, ultrasonic meters have difficultymeasuring volumetric flow rate when measuring aerated fluids. The gasbubbles scatter the ultrasonic waves and therefore, provide aninaccurate or no output at all.

Similarly, an array-based flow meter that uses an array of sensorsdisposed along the pipe for measuring vortical disturbances and/oracoustic waves propagating through the flow, are suitable for someapplications and not as suitable for other applications. The array-basedflow meter and the ultrasonic meter have common applications that areboth suitable for use, however, in other instances, the ultrasonic meterfunctions better than the array-based meter in some applications and thearray-based flow meter functions better than the ultrasonic meter inother applications. The present invention combines the two technologiesinto a single flow meter to provide a flow meter capable of functions ina great number of applications than each flow meter can function alone.

SUMMARY OF THE INVENTION

Objects of the present invention include providing a flow measuringapparatus having a dual function of measuring the parameters of thefluid flow using an array of strain-based sensor and/or ultrasonicsensors to provide a more robust flow measuring apparatus for flows ofvarying characteristics and process environments.

In one aspect of the present invention, an apparatus for measuring aprocess flow flowing within a pipe is provided. The apparatus includesat least two strain sensors disposed at different axial locations alongthe pipe. Each of the strain sensors provides a respective pressuresignal indicative of a pressure disturbance within the pipe at acorresponding axial position. At least one ultrasonic sensor is disposedon the pipe that provide a signal indicative of a parameter of theprocess flow. A signal processor, responsive to said pressure signalsand ultrasonic signal, provides a first signal indicative of a velocityof a pressure field moving with the process flow and/or provides asecond signal indicative of a speed of sound propagating through theprocess flow.

The foregoing and other objects, features and advantages of the presentinvention will become more apparent in light of the following detaileddescription of exemplary embodiments thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a flow measurement apparatus having anarray of strain-based sensors and an array of ultrasonic sensors forproviding a dual function in accordance with the present invention.

FIG. 2 is a cross-sectional view of a pipe having a turbulent fluid flowor mixture flowing therein, the flow having coherent structures therein,namely acoustic waves and vortical disturbances, in accordance with thepresent invention.

FIG. 3 is a schematic diagram of a flow logic of an array processor of aflow measuring apparatus in accordance with the present invention.

FIG. 4 is a schematic diagram of a speed of sound (SOS) logic of anarray processor of a flow measuring apparatus in accordance with thepresent invention.

FIG. 5 is a kω plot of data processed from an apparatus embodying thepresent invention that illustrates the slope of a convective ridge, anda plot of the optimization function of the convective ridge, inaccordance with the present invention.

FIG. 6 is a kω plot of data processed from an apparatus embodying thepresent invention that illustrates the slopes of a pair of acousticridges, in accordance with the present invention.

FIG. 7 is a plot of mixture sound speed as a function of gas volumefraction for a 5% consistency slurry over a range of process pressures,in accordance with the present invention.

FIG. 8 is a plot of sound speed as a function of frequency forair/particle mixtures with fixed particle size and varyingair-to-particle mass ratio in accordance with the present invention.

FIG. 9 is a plot of sound speed as a function of frequency forair/particle mixtures with varying particle size where theair-to-particle mass ratio is fixed in accordance with the presentinvention.

FIG. 10 is a schematic diagram of another embodiment of a flowmeasurement apparatus having an ultrasonic sensor and an array ofstrain-based sensors for providing a dual function in accordance withthe present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 illustrates a schematic diagram of a flow measurement apparatus10 that includes a sensing device (sensor head) 16 mounted to a pipe 14and a processing unit or array processor (transmitter) 24. The apparatus10 measures a characteristic or parameter of a single phase fluid (e.g.,gas and liquid) and/or multiphase fluids 12 (e.g., gas/liquid mixtures,liquid/solid mixtures, gas/solid mixtures, steam, pulp and paperslurries, and aerated liquids and mixtures) flowing through the pipe 14.Specifically, the flow characteristics and flow parameters determinedinclude the volumetric flow of the fluid, the consistency or compositionof the fluid, the density of the fluid, the Mach number of the fluid,the size of particle flowing through the fluid, the air/mass ratio ofthe fluid, velocity of the flow, volumetric flow rate, gas volumefraction of the flow, the speed of sound propagating through the flow,and/or the percentage of entrained air within a liquid or slurry.

For instance, the apparatus 10, in accordance with the presentinvention, can determine the speed at which sound (i.e., acoustic wave90 in FIG. 2) propagates through the fluid flow 12 within a pipe 14 tomeasure particular characteristics of the single or multi-phase fluids.The apparatus may also determine the speed at which pressuredisturbances propagate through the pipe 14 to determine the velocity ofthe fluid flow 12. The pressure disturbances may be in the form ofvortical disturbances 88 (e.g., turbulent eddies FIG. 2) or otherpressure disturbances that convect (or propagate) with the flow. Tosimplify the explanation of the present invention, the flow propagatingthrough the pipe will be referred to as a process flow with theunderstanding that the fluid or process flow 12 may be a single phase ormulti-phase flow, as described hereinbefore.

The sensing device 16 comprises an array of strain-based sensors orpressure sensors 18-21 for measuring the unsteady pressures produced byvortical disturbances within the pipe and/or speed of sound propagatingthrough the flow, which are indicative of parameters and/orcharacteristics of the process flow 12. The sensing device 16 furtherincludes an array of ultrasonic sensors 22-23, each of which having atransmitter 40 and a receiver 42, to also measure a parameter of theflow 12.

The pressure signals P₁(t)-P_(N)(t) and ultrasonic signalsS₁(t)-S_(N)(t) are provided to the processing unit 24, which digitizesthe signals and computes the appropriate flow parameter(s). A cableelectronically connects the sensing device 16 to the processing unit 24.The analog pressure sensor signals P₁(t)-P_(N)(t) are typically 4-20 mAcurrent loop signals.

The measurement apparatus 10 may be programmed to provide a flow outputparameter 29 corresponding to the pressure signals and/or ultrasonicsignals in response to an input/command from an external source, such ascontrol system (not shown) or a user. This capability enables a user toselectively process the input pressure and ultrasonic signals to providean accurate measurement of the fluid flow 12. For example, the outputmeasurements 29 may be determined using the pressure signals of thepressure sensors 18-21 for conditions when the fluid flow is aerated. Inanother example, the output measurements 29 may be determined using theultrasonic signals of the ultrasonic sensors 22-25 when the fluid flowhas no or very little entrained gas, and/or when the pipe is vibratingat a relatively high level. As one skilled in the art can appreciate,the present invention allows a user to install one meter on the pipe andmeasure parameters of the flow under different operating conditions andflow conditions. The configuration of the apparatus may be static, inother words set by the user at installation, or dynamic wherein the useror control system may dynamic switch between (or simultaneously measure)the ultrasonic sensors and the pressure sensors. The processing unit 24may also provide intelligence that will switch between utilization ofthe pressure sensors and ultrasonic sensors when sensing degradation ofthe output measurement or other external parameter (e.g., vibration).

The array of pressure sensors 18-21 comprises an array of at least twopressure sensors 18,19 spaced axially along the outer surface 17 of thepipe 14, having a process flow 12 propagating therein. The pressuresensors 18-21 may be clamped onto or generally removably mounted to thepipe by any releasable fastener, such as bolts, screws and clamps.Alternatively, the sensors may be permanently attached to or integral(e.g., embedded) with the pipe 14. The array of sensors of the sensingdevice 16 may include any number of pressure sensors 18-21 greater thantwo sensors, such as three, four, eight, sixteen or N number of sensorsbetween two and twenty-four sensors. Generally, the accuracy of themeasurement improves as the number of sensors in the array increases.The degree of accuracy provided by the greater number of sensors isoffset by the increase in complexity and time for computing the desiredoutput parameter of the flow. Therefore, the number of sensors used isdependent at least on the degree of accuracy desired and the desiredupdate rate of the output parameter provided by the apparatus 10. Thepressure sensors 18-19 measure the unsteady pressures produced byacoustic waves propagating through the flow and/or pressure disturbances(e.g., vortical eddies) that convect with the flow within the pipe 14,which are indicative of the SOS propagating through the fluid flow 12 inthe pipe and the velocity of disturbances propagating through the flow12 of the mixture 12, respectively. The output signals (P₁(t)-P_(N)(t))of the pressure sensors 18-21 are provided to a signal amplifier 39 thatamplifies the signals generated by the pressure sensors 18-21. Theprocessing unit 24 processes the pressure measurement dataP₁(t)-P_(N)(t) and determines the desired parameters and characteristicsof the flow 12, as described hereinbefore.

The apparatus 10 also contemplates providing one or more acousticsources 27 to enable the measurement of the speed of sound propagatingthrough the flow for instances of acoustically quiet flow. The acousticsource may be a device that taps or vibrates on the wall of the pipe,for example. The acoustic sources may be disposed at the input end ofoutput end of the array of sensors 18-21, or at both ends as shown. Oneshould appreciate that in most instances the acoustics sources are notnecessary and the apparatus passively detects the acoustic ridgeprovided in the flow 12, as will be described in greater detailhereinafter. The passive noise includes noise generated by pumps,valves, motors, and the turbulent mixture itself.

As suggested and further described in greater detail hereinafter, theapparatus 10 has the ability to measure the speed of sound (SOS) andflow rate (or velocity) using one or both of the following techniquesdescribed herein below:

-   -   1) Determining the speed of sound of acoustical disturbances or        sound waves propagating through the flow 12 using the array of        pressure sensors 18-21, and/or    -   2) Determining the velocity of pressure disturbances (e.g.,        vortical eddies) propagating through the flow 12 using the array        of pressure sensors 18-21.

Generally, the first technique measures unsteady pressures created byacoustical disturbances propagating through the flow 12 to determine thespeed of sound (SOS) propagating through the flow. Knowing the pressureand/or temperature of the flow and the speed of sound of the acousticdisturbances or waves, the processing unit 24 can determine thevolumetric flow of the fluid, the consistency or composition of thefluid, the density of the fluid, the Mach number of the fluid, theaverage size of particles flowing through the fluid, the air/mass ratioof the fluid, and/or the percentage of entrained air within a liquid orslurry, such as that described in U.S. patent application Ser. No.10/349,716, filed Jan. 23, 2003, U.S. patent application Ser. No.10/376,427, filed Feb. 26, 2003, U.S. patent application Ser. No.10/762,410, filed Jan. 21, 2004, which are all incorporated byreference.

The second technique measures the velocities associated with unsteadyflow fields and/or pressure disturbances, such as that created byvertical disturbances or “eddies” 88 (see FIG. 2), that convect with theprocess flow 12 to determine the velocity of the process flow. Thepressure sensors 18-21 measure the unsteady pressures P₁-P_(N) createdby the vortical disturbances 88, for example, as these disturbancesconvect with the flow 12 through the pipe 14 in a known manner, as shownin FIG. 2. Therefore, the velocity of these vortical disturbances isrelated to the velocity of the flow 12 and hence the volumetric flowrate may be determined, as will be described in greater detailhereinafter.

As shown in FIG. 1, the present invention contemplates a flowmeasurement apparatus 10 that combines the functionality of an apparatusfor measuring the velocity of the process flow and an apparatus formeasuring the speed of sound propagating through the flow within a pipe.The pressure signals P₁(t)-P_(N)(t) of the array of sensors 18-21 of thesensing device 16 are provided to an array processor 31 that includesflow logic 32 for determining the velocity and/or the volumetric flow ofthe fluid 12 and includes speed of sound (SOS) logic 34 for determiningthe composition of the flow, the average size of particles within theflow, the air/mass ratio of the flow, phase fraction of the flow, and/orthe speed of sound propagating through the flow.

As shown in FIG. 2, an apparatus 10 embodying the present invention hasan array of at least two strain-based or pressure sensors 18,19, locatedat two locations x₁,x₂ axially along the pipe 14 for sensing respectivestochastic signals propagating between the sensors 18,19 within the pipeat their respective locations. Each sensor 18,19 provides a signalindicating an unsteady pressure at the location of each sensor, at eachinstant in a series of sampling instants. One will appreciate that thesensor array may include more than two pressure sensors as depicted bypressure sensor 20,21 at location x₃,x_(N). The pressure generated bythe convective pressure disturbances (e.g., eddies 88) and acousticwaves 90 (see FIG. 2) may be measured through strained-based sensorsand/or pressure sensors 18-21. The pressure sensors 18-21 provide analogpressure time-varying signals P₁(t),P₂(t),P₃(t),P_(N)(t) to the signalprocessing unit 24

The Flow Logic 32 of the processing unit 24 as shown in FIG. 3 receivesthe pressure signals from the array of sensors 18-21. A data acquisitionunit 40 (e.g., A/D converter) converts the analog signals to respectivedigital signals. The digitized signals are provided to Fast FourierTransform (FFT) logic 42. The FFT logic calculates the Fourier transformof the digitized time-based input signals P₁(t)-P_(N)(t) and providescomplex frequency domain (or frequency based) signals P₁(ω), P₂(ω),P₃(ω), P_(N)(ω) indicative of the frequency content of the inputsignals. Instead of FFT's, any other technique for obtaining thefrequency domain characteristics of the signals P₁(t)-P_(N)(t), may beused. For example, the cross-spectral density and the power spectraldensity may be used to form one or more frequency domain transferfunctions (or frequency responses or ratios) discussed hereinafter.

One technique of determining the convection velocity of the turbulenteddies 88 within the process flow 12 is by characterizing a convectiveridge of the resulting unsteady pressures using an array of sensors orother beam forming techniques, similar to that described in U.S. Pat.No. 6,889,526 and U.S. Pat. No. 6,609,069, which are incorporated hereinby reference.

A data accumulator 44 accumulates the frequency signals P₁(ω)-P_(N)(ω)over a sampling interval, and provides the data to an array processor46, which performs a spatial-temporal (two-dimensional) transform of thesensor data, from the xt domain to the k-ω domain, and then calculatesthe power in the k-ω plane, as represented by a k-ω plot.

The array processor 46 uses standard so-called beam forming, arrayprocessing, or adaptive array-processing algorithms, i.e. algorithms forprocessing the sensor signals using various delays and weighting tocreate suitable phase relationships between the signals provided by thedifferent sensors, thereby creating phased antenna array functionality.In other words, the beam forming or array processing algorithmstransform the time domain signals from the sensor array into theirspatial and temporal frequency components, i.e. into a set of wavenumbers given by k=2π/λ where λ is the wavelength of a spectralcomponent, and corresponding angular frequencies given by ω=2πν.

The prior art teaches many algorithms of use in spatially and temporallydecomposing a signal from a phased array of sensors, and the presentinvention is not restricted to any particular algorithm. One particularadaptive array processing algorithm is the Capon method/algorithm. Whilethe Capon method is described as one method, the present inventioncontemplates the use of other adaptive array processing algorithms, suchas MUSIC algorithm. The present invention recognizes that suchtechniques can be used to determine flow rate, i.e. that the signalscaused by a stochastic parameter convecting with a flow are timestationary and have a coherence length long enough that it is practicalto locate sensor units apart from each other and yet still be within thecoherence length.

Convective characteristics or parameters have a dispersion relationshipthat can be approximated by the straight-line equation,k=ω/u,

where u is the convection velocity (flow velocity). A plot of k-ω pairsis obtained from a spectral analysis of sensor samples associated withconvective parameters. The pairings are portrayed so that the energy ofthe disturbance spectrally corresponding to the pairings can bedescribed as a substantially straight ridge, a ridge that in turbulentboundary layer theory is called a convective ridge. What is being sensedare not discrete events of turbulent eddies, but rather a continuum ofpossibly overlapping events forming a temporally stationary, essentiallywhite process over the frequency range of interest. In other words, theconvective eddies 88 are distributed over a range of length scales andhence temporal frequencies.

To calculate the power in the k-ω plane, as represented by a k-ω plot(see FIG. 5) of either the signals, the array processor 46 determinesthe wavelength and so the (spatial) wavenumber k, and also the(temporal) frequency and so the angular frequency ω, of various of thespectral components of the stochastic parameter. There are numerousalgorithms available in the public domain to perform thespatial/temporal decomposition of arrays of sensor units 18-21.

The present invention may use temporal and spatial filtering toprecondition the signals to effectively filter out the common modecharacteristics P_(common mode) and other long wavelength (compared tothe sensor spacing) characteristics in the pipe 14 by differencingadjacent sensors and retaining a substantial portion of the stochasticparameter associated with the flow field and any other short wavelength(compared to the sensor spacing) low frequency stochastic parameters.

In the case of suitable turbulent eddies 88 (see FIG. 2) being present,the power in the k-ω plane shown in a k-ω plot of FIG. 5 shows aconvective ridge 100. The convective ridge represents the concentrationof a stochastic parameter that convects with the flow and is amathematical manifestation of the relationship between the spatialvariations and temporal variations described above. Such a plot willindicate a tendency for k-ω pairs to appear more or less along a line100 with some slope, the slope indicating the flow velocity.

Once the power in the k-ω plane is determined, a convective ridgeidentifier 48 uses one or another feature extraction method to determinethe location and orientation (slope) of any convective ridge 100 presentin the k-ω plane. In one embodiment, a so-called slant stacking methodis used, a method in which the accumulated frequency of k-ω pairs in thek-ω plot along different rays emanating from the origin are compared,each different ray being associated with a different trial convectionvelocity (in that the slope of a ray is assumed to be the flow velocityor correlated to the flow velocity in a known way). The convective ridgeidentifier 48 provides information about the different trial convectionvelocities, information referred to generally as convective ridgeinformation.

The analyzer 50 examines the convective ridge information including theconvective ridge orientation (slope). Assuming the straight-linedispersion relation given by k=ω/u, the analyzer 50 determines the flowvelocity, Mach number and/or volumetric flow. The volumetric flow isdetermined by multiplying the cross-sectional area of the inside of thepipe with the velocity of the process flow.

As shown in FIG. 4, the SOS Logic 34 includes a second data acquisitionunit 54 that digitizes the pressure signals P₁(t)-P_(N)(t) associatedwith the acoustic waves 14 propagating through the pipe 14. Similar tothe FFT logic 42, an FFT logic 56 calculates the Fourier transform ofthe digitized time-based input signals P₁(t)-P_(N)(t) and providescomplex frequency domain (or frequency based) signalsP₁(ω),P₂(ω),P₃(ω),P_(N)(ω) indicative of the frequency content of theinput signals.

A data accumulator 58 accumulates the signals P₁(t)-P_(N)(t) from thesensors, and provides the data accumulated over a sampling interval toan array processor 60, which performs a spatial-temporal(two-dimensional) transform of the sensor data, from the xt domain tothe k-ω domain, and then calculates the power in the k-ω plane, asrepresented by a k-ω plot, similar to that provided by the convectivearray processor 46.

To calculate the power in the k-ω plane, as represented by a k-ω plot(see FIG. 6) of either the signals or the differenced signals, the arrayprocessor 60 determines the wavelength and so the (spatial) wavenumberk, and also the (temporal) frequency and so the angular frequency ω, ofvarious of the spectral components of the stochastic parameter. Thereare numerous algorithms available in the public domain to perform thespatial/temporal decomposition of the array of pressure sensors 18-21.

In the case of suitable acoustic waves 90 being present in both axialdirections, the power in the k-ω plane shown in a k-ω plot of FIG. 6 sodetermined will exhibit a structure that is called an acoustic ridge110,112 in both the left and right planes of the plot, wherein one ofthe acoustic ridges 110 is indicative of the speed of sound traveling inone axial direction and the other acoustic ridge 112 being indicative ofthe speed of sound traveling in the other axial direction.

The acoustic ridges represent the concentration of a stochasticparameter that propagates through the flow and is a mathematicalmanifestation of the relationship between the spatial variations andtemporal variations described above. Such a plot will indicate atendency for k-ω pairs to appear more or less along a line 110,112 withsome slope, the slope indicating the speed of sound. The power in thek-ω plane so determined is then provided to an acoustic ridge identifier62, which uses one or another feature extraction method to determine thelocation and orientation (slope) of any acoustic ridge present in theleft and right k-ω plane. The velocity may be determined by using theslope of one of the two acoustic ridges 110,112 or averaging the slopesof the acoustic ridges 110,112.

Finally, information including the acoustic ridge orientation (slope) isused by an analyzer 64 to determine the flow parameters 29 relating tomeasured speed of sound, such as the consistency or composition of theflow, the density of the flow, the average size of particles in theflow, the air/mass ratio of the flow, gas volume fraction of the flow,the speed of sound propagating through the flow, and/or the percentageof entrained air within the flow.

Similar to the array processor 46, the array processor 60 uses standardso-called beam forming, array processing, or adaptive array-processingalgorithms, i.e. algorithms for processing the sensor signals usingvarious delays and weighting to create suitable phase relationshipsbetween the signals provided by the different sensors, thereby creatingphased antenna array functionality. In other words, the beam forming orarray processing algorithms transform the time domain signals from thesensor array into their spatial and temporal frequency components, i.e.into a set of wave numbers given by k=2π/λ where λ is the wavelength ofa spectral component, and corresponding angular frequencies given byω=2πν.

One such technique of determining the speed of sound propagating throughthe flow 12 is using array processing techniques to define an acousticridge in the k-ω plane as shown in FIG. 6. The slope of the acousticridge is indicative of the speed of sound propagating through the flow12. The speed of sound (SOS) is determined by applying sonar arrayingprocessing techniques to determine the speed at which the onedimensional acoustic waves propagate past the axial array of unsteadypressure measurements distributed along the pipe 14.

The apparatus 10 of the present invention measures the speed of sound(SOS) of one-dimensional sound waves propagating through the mixture todetermine the gas volume fraction of the mixture. It is known that soundpropagates through various mediums at various speeds in such fields asSONAR and RADAR fields. The speed of sound propagating through the pipeand flow 12 may be determined using a number of known techniques, suchas those set forth in U.S. patent application Ser. No. 09/344,094, filedJun. 25, 1999, now U.S. Pat. No. 6,354,147; U.S. patent application Ser.No. 10/795,111, filed Mar. 4, 2004; U.S. patent application Ser. No.09/997,221, filed Nov. 28, 2001, now U.S. Pat. No. 6,587,798; U.S.patent application Ser. No. 10/007,749, filed Nov. 7, 2001, and U.S.patent application Ser. No. 10/762,410, filed Jan. 21, 2004, each ofwhich are incorporated herein by reference.

While the sonar-based flow meter using an array of sensors to measurethe speed of sound of an acoustic wave propagating through the mixtureis shown and described, one will appreciate that any means for measuringthe speed of sound of the acoustic wave may be used to determine theentrained gas volume fraction of the mixture/fluid or othercharacteristics of the flow described hereinbefore.

The analyzer 64 of the acoustic processing unit 53 provides outputsignals indicative of characteristics of the process flow 12 that arerelated to the measured speed of sound (SOS) propagating through theflow 12. For example, to determine the gas volume fraction (or phasefraction), the analyzer 64 assumes a nearly isothermal condition for theflow 12. As such the gas volume fraction or the void fraction is relatedto the speed of sound by the following quadratic equation:Ax ² +Bx+C=0

wherein x is the speed of sound, A=1+rg/rl*(K_(eff)/P−1)−K_(eff)/P,B=K_(eff)/P−2+rg/rl; C=1−K_(eff)/rl*a_(meas)^2); Rg=gas density,rl=liquid density, K_(eff)=effective K (modulus of the liquid andpipewall), P=pressure, and a_(meas)=measured speed of sound.

Effectively,Gas Volume Fraction (GVF)=(−B+sqrt(B^2−4*A*C))/(2*A)

Alternatively, the sound speed of a mixture can be related to volumetricphase fraction (φ_(i)) of the components and the sound speed (a) anddensities (ρ) of the component through the Wood equation.

$\frac{1}{\rho_{mix}a_{{mix}_{\infty}}^{2}} = {{\sum\limits_{i = 1}^{N}{\frac{\phi_{i}}{\rho_{i}a_{i}^{2}}\mspace{14mu}{where}\mspace{14mu}\rho_{mix}}} = {\sum\limits_{i = 1}^{N}{\rho_{i}\phi_{i}}}}$

One dimensional compression waves propagating within a mixture 12contained within a pipe 14 exert an unsteady internal pressure loadingon the pipe. The degree to which the pipe displaces as a result of theunsteady pressure loading influences the speed of propagation of thecompression wave. The relationship among the infinite domain speed ofsound and density of a mixture; the elastic modulus (E), thickness (t),and radius (R) of a vacuum-backed cylindrical conduit; and the effectivepropagation velocity (a_(eff)) for one dimensional compression is givenby the following expression:

$\begin{matrix}{a_{eff} = \frac{1}{\sqrt{{1/a_{{mix}_{\infty}}^{2}} + {\rho_{mix}\frac{2R}{Et}}}}} & \left( {{eq}\mspace{20mu} 1} \right)\end{matrix}$

The mixing rule essentially states that the compressibility of a mixture(1/(ρa²)) is the volumetrically-weighted average of thecompressibilities of the components. For gas/liquid mixtures 12 atpressure and temperatures typical of paper and pulp industry, thecompressibility of gas phase is orders of magnitudes greater than thatof the liquid. Thus, the compressibility of the gas phase and thedensity of the liquid phase primarily determine mixture sound speed, andas such, it is necessary to have a good estimate of process pressure tointerpret mixture sound speed in terms of volumetric fraction ofentrained gas. The effect of process pressure on the relationshipbetween sound speed and entrained air volume fraction is shown in FIG.7.

As described hereinbefore, the apparatus 10 of the present inventionincludes the ability to accurately determine the average particle sizeof a particle/air or droplet/air mixture within the pipe 14 and the airto particle ratio. Provided there is no appreciable slip between the airand the solid coal particle, the propagation of one dimensional soundwave through multiphase mixtures is influenced by the effective mass andthe effective compressibility of the mixture. For an air transportsystem, the degree to which the no-slip assumption applies is a strongfunction of particle size and frequency. In the limit of small particlesand low frequency, the no-slip assumption is valid. As the size of theparticles increases and the frequency of the sound waves increase, thenon-slip assumption becomes increasing less valid. For a given averageparticle size, the increase in slip with frequency causes dispersion,or, in other words, the sound speed of the mixture changes withfrequency. With appropriate calibration the dispersive characteristic ofa mixture 12 will provide a measurement of the average particle size, aswell as the air to particle ratio (particle/fluid ratio) of the mixture.

In accordance with the present invention the dispersive nature of thesystem utilizes a first principles model of the interaction between theair and particles. This model is viewed as being representative of aclass of models that seek to account for dispersive effects. Othermodels could be used to account for dispersive effects without alteringthe intent of this disclosure (for example, see the paper titled“Viscous Attenuation of Acoustic Waves in Suspensions” by R. L. Gibson,Jr. and M. N. Toksöz), which is incorporated herein by reference. Themodel allows for slip between the local velocity of the continuous fluidphase and that of the particles.

The following relation can be derived for the dispersive behavior of anidealized fluid particle mixture.

${a_{mix}(\omega)} = {a_{j}\sqrt{\frac{1}{1 + \frac{\varphi_{p}\rho_{p}}{\rho_{f}\left( {1 + {\omega^{2}\frac{\rho_{p}^{2}v_{p}^{2}}{K^{2}}}} \right)}}}}$In the above relation, the fluid SOS, density (ρ) and viscosity (φ) arethose of the pure phase fluid, v_(p) is the volume of individualparticles and φ_(p) is the volumetric phase fraction of the particles inthe mixture.

Two parameters of particular interest in steam processes andair-conveyed particles processes are particle size and air-to-fuel massratio or steam quality. To this end, it is of interest to examine thedispersive characteristics of the mixture as a function of these twovariables. FIGS. 8 and 9 show the dispersive behavior in relations tothe speed of sound for coal/air mixtures with parameters typical ofthose used in pulverized coal deliver systems.

In particular FIG. 8 shows the predicted behavior for nominally 50 μmsize coal in air for a range of air-to-fuel ratios. As shown, the effectof air-to-fuel ratio is well defined in the low frequency limit.However, the effect of the air-to-fuel ratio becomes indistinguishableat higher frequencies, approaching the sound speed of the pure air athigh frequencies (above ˜100 Hz).

Similarly, FIG. 9 shows the predicted behavior for a coal/air mixturewith an air-to-fuel ratio of 1.8 with varying particle size. This figureillustrates that particle size has no influence on either the lowfrequency limit (quasi-steady) sound speed, or on the high frequencylimit of the sound speed. However, particle size does have a pronouncedeffect in the transition region.

FIGS. 8 and 9 illustrate an important aspect of the present invention.Namely, that the dispersive properties of dilute mixtures of particlessuspended in a continuous fluid can be broadly classified into threefrequency regimes: low frequency range, high frequency range and atransitional frequency range. Although the effect of particle size andair-to-fuel ratio are inter-related, the predominant effect ofair-to-fuel ratio is to determine the low frequency limit of the soundspeed to be measured and the predominate effect of particle size is todetermine the frequency range of the transitional regions. As particlesize increases, the frequency at which the dispersive properties appeardecreases. For typical pulverized coal applications, this transitionalregion begins at fairly low frequencies, ˜2 Hz for 50 μm size particles.

Given the difficulties measuring sufficiently low frequencies to applythe quasi-steady model and recognizing that the high frequency soundspeed contains no direct information on either particle size orair-to-fuel ratio, it becomes apparent that the dispersivecharacteristics of the coal/air mixture should be utilized to determineparticle size and air-to-fuel ratio based on speed of soundmeasurements.

Some or all of the functions within the processing unit 24 may beimplemented in software (using a microprocessor or computer) and/orfirmware, or may be implemented using analog and/or digital hardware,having sufficient memory, interfaces, and capacity to perform thefunctions described herein.

While data acquisition units 40,54, FFT logic 42,56, data accumulators44,58, array processors 46,60 and ridge identifiers 48, 62 are shown asseparate elements or separate software/processing routines, one willappreciate that each of these elements may be common and able to processthe data associated with both the pressure signals associated with thespeed of sound and the pressures that convect with the process flow.

As shown in FIG. 1, the measurement apparatus 10 includes a sensingdevice 16 comprising an array of ultrasonic sensor units 22-25. Eachsensor unit comprises a pair of ultrasonic sensors 40,42, one of whichfunctions as a transmitter (Tx) 40 and the other as a receiver (Rx) 42.The sensor units 22-25 are spaced axially along the outer surface 17 ofthe pipe 14 having a process flow 12 propagating therein. The pair ofsensors 40,42 is diametrically disposed on the pipe at predeterminedlocations along the pipe to provide a through transmissionconfiguration, such that the sensors transmit and receive an ultrasonicsignal that propagates through the fluid substantially orthogonal to thedirection of the flow of the fluid within the pipe. The ultrasonicmeasurement portion of the present invention is similar to that shown inU.S. patent application Ser. No. 10/756,977 filed on Jan. 13, 2004,which is incorporated herein by reference.

As shown in FIG. 1, each pair of ultrasonic sensors 40,42 measures atransit time (i.e., time of flight (TOF), or phase modulation) of anultrasonic signal propagating through the fluid 12 from the transmittingsensor 40 to the receiving sensor 42. The transit time measurement orvariation is indicative of a coherent properties that convect with theflow within the pipe (e.g., vortical disturbances, inhomogenietieswithin the flow, temperature variations, bubbles, particles, pressuredisturbances), which are indicative of the velocity of the process flow12. The ultrasonic sensors may operate at any frequency, however, it hasbe found that the higher frequency sensors are more suitable for singlephase fluids while lower frequency sensors are more suitable formultiphase fluids. The optimum frequency of the ultrasonic sensor isdependent on the size or type of particle or substance propagating withthe flow 12. For instance, the larger the air bubbles in an aeratedfluid the lower the desirable frequency of the ultrasonic signal.Examples of frequency used for a flow meter embodying the presentinvention are 1 MHz and 5 MHz. The ultrasonic sensors may also provide apulsed, chirped or continuous signal through the fluid flow 12. Anexample of the sensors 40,42 that may be used are Model no. 113-241-591,manufactured by Krautkramer.

An ultrasonic signal processor 37 fires the sensors 40 in response to afiring signal 39 from the transmitter 24 and receives the ultrasonicoutput signals S₁(t)-S_(N)(t) from the sensors 42. The signal processor37 processes the data from each of the sensor units 18-21 to provide ananalog or digital output signal T₁(t)-T_(N)(t) indicative of the time offlight or transit time of the ultrasonic signal through the fluid. Thesignal processor 37 may also provide an output signal indicative of theamplitude (or attenuation) of the ultrasonic signals. One such signalprocessor is model no. USPC 2100 manufactured by Krautkramer UltrasonicSystems. Measuring the amplitude of ultrasonic signal is particularlyuseful and works best for measuring the velocity of a fluid thatincludes a substance in the flow (e.g., multiphase fluid or slurry).

The output signals (T₁(t)-T_(N)(t)) of the ultrasonic signal processor37 are provided to the processor 24, which processes the transit timemeasurement data to determine the volumetric flow rate. The transit timeor time of flight measurement is defined by the time it takes for anultrasonic signal to propagate from the transmitting sensor 40 to therespective receiving sensor 42 through the pipe wall and the fluid 12.The effect of the vortical disturbances (and/or other inhomogenitieswithin the fluid) on the transit time of the ultrasonic signal is todelay or speed up the transit time. Therefore, each sensing unit 22-25provides a respective output signal T₁(t)-T_(N)(t) indicative of thevariations in the transit time of the ultrasonic signals propagatingorthogonal to the direction of the fluid 12. The measurement is derivedby interpreting the convecting coherent property and/or characteristicwithin the process piping using at least two sensor units 22,23. Theultrasonic sensors 22-25 may be “wetted” or clamped onto the outersurface 17 of the pipe 14 (e.g. contact or non-contact sensor).

In one example, the flow meter 10 measures the volumetric flow rate bydetermining the velocity of vortical disturbances or “eddies” 88 (seeFIG. 2) propagating with the flow 12 using the array of ultrasonicsensors 22-25. The flow meter 10 measures the velocities associated withunsteady flow fields created by vortical disturbances or “eddies” 88 andother inhomogenities to determine the velocity of the flow 12. Theultrasonic sensor units 22-25 measure the transmit time T₁(t)-T_(N)(t)of the respective ultrasonic signals between each respective pair ofsensors 40,42, which vary due to the vortical disturbances as thesedisturbances convect within the flow 12 through the pipe 14 in a knownmanner. Therefore, the velocity of these vortical disturbances isrelated to the velocity of the flow 12 and hence the volumetric flowrate may be determined, as will be described in greater detailhereinafter. The volumetric flow is determined by multiplying thevelocity of the fluid by the cross-sectional area of the pipe.

The Flow Logic 65 processes the ultrasonic signals in a substantiallysimilar way as that described for the Flow Logic 32 for the pressuresignals shown in FIG. 3. Consequently, the pressure signals and theultrasonic signals may be processed using a single processor to performthe Flow Logic 32 and the Flow Logic 65 or may be separate processors toenable simultaneous processing of the pressure and ultrasonic signals.

While each of the ultrasonic sensor units 22-25 of FIG. 1 comprises apair of ultrasonic sensors (transmitter and receiver) 40,42diametrically-opposed to provide through transmission, the presentinvention contemplates that one of the ultrasonic sensors 40,42 of eachsensor unit 22-25 may be offset axially such that the ultrasonic signalfrom the transmitter sensor has an axial component in its propagationdirection.

The present invention also contemplates the sensor units 22-25 of thesensing device 16 may be configured in a pulse/echo configuration. Inthis embodiment, each sensing unit 22-25 comprises one ultrasonic sensorthat transmits an ultrasonic signal through the pipe wall and fluidsubstantially orthogonal to the direction of flow and receives areflection of the ultrasonic signal reflected back from the wall of thepipe to the ultrasonic sensor.

The sensing device 16 may be configured to function in a pitch and catchconfiguration. In this embodiment, each sensor unit 22-25 comprises apair of ultrasonic sensors (transmitter, receiver) 40, 42 disposedaxially along the pipe disposed on the same side of the pipe at apredetermined distance apart. Each transmitter sensor 40 provides anultrasonic signal a predetermined angle into the flow 12. The ultrasonicsignal propagates through the fluid 12 and reflects off the innersurface of the pipe 14 and reflects the ultrasonic signal back throughthe fluid to the respective receiver sensor 42.

As shown in FIG. 10, while the ultrasonic sensor portion 51 comprises anarray of ultrasonic sensor units 22-25 (see FIG. 1), the presentinvention contemplates that any ultrasonic meter or sensing portion maybe used. The ultrasonic meter may be any meter within any of the threeclasses of flow meters that utilize ultrasonic transducers, whichinclude transit time ultrasonic flow meters (TTUF), doppler ultrasonicflow meters (DUF), and cross correlation ultrasonic flow meters (CCUF).A transit time ultrasonic meter is illustrated in FIG. 10.

The ultrasonic sensor portion may be any known ultra-sonic flow meter,such as U.S. Pat. Nos. 2,874,568; 4,004,461; 6,532,827; 4,195,517;5,856,622; and 6,397,683, which are all incorporated herein byreference.

The array-based flow meter is similar to that described in U.S. patentapplication Ser. No. 10/007,749 filed Nov. 7, 2001, U.S. patentapplication Ser. No. 10/007,736 filed Nov. 8, 2001, U.S. Pat. No.6,587,798, filed on Nov. 28, 2001, U.S. Provisional Patent ApplicationSer. No. 60/359,785 filed Feb. 26, 2002. U.S. Provisional PatentApplication Ser. No. 60/425,436 filed Nov. 12, 2002, U.S. patentapplication Ser. No. 09/729,994, filed Dec. 4, 2000, and U.S. patentapplication, Ser. No. 10,875,857 filed Jun. 24, 2004, which are allincorporated herein by reference.

While a single array processor 32 is shown to receive and process inputsignals from the pressure sensors 18-21 and the ultrasonic sensors22-25, the present invention contemplates that an array processor may bededicated to each of the array of pressure sensor 18-21 and the array ofultra-sonic sensors 22-25.

In one embodiment as shown in FIG. 1, each of the pressure sensors 18-21may include a piezoelectric film 50 attached to a unitary multi-bandstrap 52 to measure the unsteady pressures of the flow 12 using eithertechnique described hereinbefore. The piezoelectric film sensors 18-21are mounted onto a unitary substrate or web which is mounted or clampedonto the outer surface 22 of the pipe 14, which will be described ingreater detail hereinafter.

The piezoelectric film sensors 18-21 include a piezoelectric material orfilm 50 to generate an electrical signal proportional to the degree thatthe material is mechanically deformed or stressed. The piezoelectricsensing element 50 is typically conformed to allow complete or nearlycomplete circumferential measurement of induced strain to provide acircumferential-averaged pressure signal. The sensors can be formed fromPVDF films, co-polymer films, or flexible PZT sensors, similar to thatdescribed in “Piezo Film Sensors Technical Manual” provided byMeasurement Specialties, Inc., which is incorporated herein byreference. A piezoelectric film sensor that may be used for the presentinvention is part number 1-1002405-0, LDT4-028K, manufactured byMeasurement Specialties, Inc. While the piezoelectric film material 50is substantially the length of the band 44, and therefore thecircumference of the pipe 14, the present invention contemplates thatthe piezoelectric film material may be disposed along a portion of theband of any length Less than the circumference of the pipe.

Piezoelectric film (“piezofilm”) 50, like piezoelectric material, is adynamic material that develops an electrical charge proportional to achange in mechanical stress. Consequently, the piezoelectric materialmeasures the strain induced within the pipe 14 due to unsteady orstochastic pressure variations (e.g., vortical and/or acoustical) withinthe process flow 12. Strain within the pipe is transduced to an outputvoltage or current by the attached piezoelectric sensor 18-21. Thepiezoelectrical material or film 50 may be formed of a polymer, such aspolarized fluoropolymer, polyvinylidene fluoride (PVDF). Thepiezoelectric film sensors are similar to that described in U.S. patentapplication Ser. No. 10/712,818, filed Nov. 12, 2003 and U.S. patentapplication Ser. No. 10/795,111, filed Mar. 4, 2004, which areincorporated herein by reference. The advantages of this clamp-ontechnique using piezoelectric film include non-intrusive flow ratemeasurements, low cost, measurement technique requires no excitationsource. One will appreciate that the sensor may be installed or mountedto the pipe 14 as individual sensors or all the sensors mounted as asingle unit as shown in FIG. 1.

The pressure sensors 18-21 of FIG. 1 described herein may be any type ofsensor, capable of measuring the unsteady (or ac or dynamic) pressuresor parameter that convects with the flow within a pipe 14, such aspiezoelectric, optical, capacitive, resistive (e.g., Wheatstone bridge),accelerometers (or geophones), velocity measuring devices, displacementmeasuring devices, ultra-sonic devices, etc. If optical pressure sensorsare used, the sensors 18-21 may be Bragg grating based pressure sensors,such as that described in U.S. patent application Ser. No. 08/925,598,entitled “High Sensitivity Fiber Optic Pressure Sensor For Use In HarshEnvironments”, filed Sep. 8, 1997, now U.S. Pat. No. 6,016,702, and inU.S. patent application Ser. No. 10/224,821, entitled “Non-IntrusiveFiber Optic Pressure Sensor for Measuring Unsteady Pressures within aPipe”, which are incorporated herein by reference. In an embodiment ofthe present invention that utilizes fiber optics as the pressure sensors14 they may be connected individually or may be multiplexed along one ormore optical fibers using wavelength division multiplexing (WDM), timedivision multiplexing (TDM), or any other optical multiplexingtechniques.

In certain embodiments of the present invention, a piezo-electronicpressure transducer may be used as one or more of the pressure sensors18-21 and it may measure the unsteady (or dynamic or ac) pressurevariations inside the pipe 14 by measuring the pressure levels inside ofthe pipe. These sensors may be ported within the pipe to make directcontact with the process flow 12. In an embodiment of the presentinvention, the sensors comprise pressure sensors manufactured by PCBPiezotronics. In one pressure sensor there are integrated circuitpiezoelectric voltage mode-type sensors that feature built-inmicroelectronic amplifiers, and convert the high-impedance charge into alow-impedance voltage output. Specifically, a Model 106B manufactured byPCB Piezotronics is used which is a high sensitivity, accelerationcompensated integrated circuit piezoelectric quartz pressure sensorsuitable for measuring low pressure acoustic phenomena in hydraulic andpneumatic systems.

It is also within the scope of the present invention that any strainsensing technique may be used to measure the variations in strain in thepipe, such as highly sensitive piezoelectric, electronic or electric,strain gages and piezo-resistive strain gages attached to the pipe 12.Other strain gages include resistive foil type gages having a race trackconfiguration similar to that disclosed U.S. patent application Ser. No.09/344,094, filed Jun. 25, 1999, now U.S. Pat. No. 6,354,147, which isincorporated herein by reference. The invention also contemplates straingages being disposed about a predetermined portion of the circumferenceof pipe 12. The axial placement of and separation distance ΔX₁, ΔX₂between the strain sensors are determined as described herein above.

It is also within the scope of the present invention that any otherstrain sensing technique may be used to measure the variations in strainin the pipe, such as highly sensitive piezoelectric, electronic orelectric, strain gages attached to or embedded in the pipe 14.

While the description has described the apparatus as two separate metersthat measure the vortical disturbances and the speed of sound,respectively, as suggested by FIG. 1, the processing could function astwo separate meters, a combination (simultaneous operation) of bothfunction, or selectively choose between operations.

The dimensions and/or geometries for any of the embodiments describedherein are merely for illustrative purposes and, as such, any otherdimensions and/or geometries may be used if desired, depending on theapplication, size, performance, manufacturing requirements, or otherfactors, in view of the teachings herein.

It should be understood that, unless stated otherwise herein, any of thefeatures, characteristics, alternatives or modifications describedregarding a particular embodiment herein may also be applied, used, orincorporated with any other embodiment described herein. Also, thedrawings herein are not drawn to scale.

Although the invention has been described and illustrated with respectto exemplary embodiments thereof, the foregoing and various otheradditions and omissions may be made therein and thereto withoutdeparting from the spirit and scope of the present invention.

1. An apparatus for measuring a process flow flowing within a pipe, theapparatus comprising: at least two strain sensors disposed at differentaxial locations along the pipe, each of the strain sensors providing arespective pressure signal indicative of pressure disturbances withinthe pipe at the corresponding axial location; at least two ultrasonicsensors disposed along the pipe that provides an ultrasonic signalindicative of a parameter of the process flow, each ultrasonic sensorcomprising a transmitter and a receiver, wherein each transmittertransmit an ultrasonic wave to the respective receiver such that therespective ultrasonic wave propagates substantially orthogonal to thedirection of the process flow; and a signal processor, responsive tosaid pressure signals and ultrasonic signal, which provides a firstsignal indicative of a velocity of a pressure field moving with theprocess flow and/or provides a second signal indicative of a speed ofsound propagating through the process flow.
 2. The apparatus of claim 1,wherein the processing unit includes a convective processing unit thatincludes an array processor that determines power in the k-ω plane, theconvective ridge in the k-ω plane, and a slope of the convective ridgeto determine one of the velocity, the mach number, and volumetric flowrate of the process flow.
 3. The apparatus of claim 1, wherein theprocessing unit includes an acoustic processing unit that includes anarray processor that determines power in the k-ω plane and determinesthe acoustic ridge in the k-ω plane.
 4. The apparatus of claim 1,wherein the pressure signals are indication of acoustic pressurespropagating axially within the flow and unsteady pressures convectingwith the flow.
 5. The apparatus of claim 1, wherein the at least twopressure sensors include one of 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,15, 16, 17, 18, 19 and 20 pressure sensors.
 6. The apparatus of claim 1,wherein the at least two ultrasonic sensors provides a respective signalindicative of a parameter of the ultrasonic wave propagating betweeneach respective transmitter and receiver.
 7. The apparatus of claim 6,wherein the processor samples the ultrasonic signals over apredetermined time period, accumulates the sampled ultrasonic signalsover a predetermined sampling period, and processes the sampledultrasonic signals to define the convective ridge in the k-ω plane. 8.The apparatus of claim 7, wherein the ultrasonic signals are indicativeof vortical disturbances with the fluid.
 9. The apparatus of claim 6,wherein the parameter of the ultrasonic signal is at least one of thesignal amplitude and the signal transit time of an ultrasonic signal.10. The apparatus of claim 6, wherein the at least two ultrasonic sensorunits include one of 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,17, 18, 19 and 20 ultrasonic sensors.
 11. The apparatus of claim 10,wherein the signal processor defines a convective ridge in the k-ω planein response to the ultrasonic signals, and determines the slope of atleast a portion of the convective ridge to determine the flow velocityof the fluid.
 12. The apparatus of claim 1, wherein the signal processorin response to an environmental condition provides one of a first outputsignal, responsive to the first signal, or a second output signal,responsive to the second signal.
 13. The apparatus of claim 12, whereinthe environmental condition is vibration on the pipe.
 14. The apparatusof claim 1, wherein the signal processor in response to a user inputsignal provides one of a first output signal, responsive to the firstsignal, or a second output signal, responsive to the second signal. 15.An apparatus for measuring a process flow flowing within a pipe, theapparatus comprising: at least two strain sensors disposed at differentaxial locations along the pipe, each of the strain sensors providing arespective pressure signal indicative of pressure disturbances withinthe pipe at the corresponding axial location; at least two ultrasonicsensors disposed along the pipe that provides an ultrasonic signalindicative of a parameter of the process flow, each ultrasonic sensorcomprising a transmitter and a receiver, wherein each transmittertransmit an ultrasonic wave to the respective receiver such that therespective ultrasonic wave propagates substantially orthogonal to thedirection of the process flow; and a signal processor which, responsiveto said ultrasonic signal, provides a first signal indicative of avelocity of the process flow; and which, responsive to said pressuresignals, provides a second signal indicative of a velocity of a pressurefield moving with the process flow and/or a third signal indicative ofthe speed of sound propagating axially through the process flow.
 16. Theapparatus of claim 15, wherein the processing unit includes a convectiveprocessing unit that includes an array processor that determines powerin the k-ω plane, the convective ridge in the k-ω plane, and a slope ofthe convective ridge to determine one of the velocity, the mach number,and volumetric flow rate of the process flow.
 17. The apparatus of claim15, wherein the processing unit includes an acoustic processing unitthat includes an array processor that determines power in the k-ω planeand determines the acoustic ridge in the k-ω plane.
 18. The apparatus ofclaim 15, wherein the pressure signals are indication of acousticpressures propagating axially within the flow and unsteady pressuresconvecting with the flow.
 19. The apparatus of claim 15, wherein the atleast two pressure sensors include one of 3, 4, 5, 6, 7, 8, 9, 10, 11,12, 13, 14, 15, 16, 17, 18, 19 and 20 pressure sensors.
 20. Theapparatus of claim 15, wherein the at least two ultrasonic sensorsprovide a respective signal indicative of a parameter of an ultrasonicsignal propagating between each respective ultrasonic transmitter andultrasonic receiver.
 21. The apparatus of claim 20, wherein the signalprocessor samples the ultrasonic signals over a predetermined timeperiod, accumulates the sampled ultrasonic signals over a predeterminedsampling period, and processes the sampled ultrasonic signals to definethe convective ridge in the k-ω plane.
 22. The apparatus of claim 21,wherein the ultrasonic signals are indicative of vortical disturbanceswith the fluid.
 23. The apparatus of claim 15, wherein the parameter ofthe ultrasonic signal is at least one of the signal amplitude and thesignal transit time of an ultrasonic signal.
 24. The apparatus of claim15, wherein the at least two ultrasonic sensor units include one of 3,4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 and 20ultrasonic sensors.
 25. The apparatus of claim 24, wherein the signalprocessor defines a convective ridge in the k-ω plane in response to theultrasonic signals, and determines the slope of at least a portion ofthe convective ridge to determine the flow velocity of the fluid. 26.The apparatus of claim 15, wherein the signal processor in response toan environmental condition provides one of a first output signal,responsive to the first signal, or a second output signal, responsive tothe second signal.
 27. The apparatus of claim 26, wherein theenvironmental condition is vibration on the pipe.
 28. The apparatus ofclaim 15, wherein the signal processor in response to a user inputsignal provides one of a first output signal, responsive to the firstsignal, or a second output signal, responsive to the second signal.